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This version is outdated by a newer approved version.DiffThis version (28 Apr 2017 15:59) is a draft.
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Table of Contents

Controlling the transceiver and transferring data

PlutoSDR runs Linux. The device drivers allowing you to control the transceiver and capture samples are therefore part of to the Linux Industrial IO (IIO) framework. IIO is a kernel subsystem for analog to digital or digital to analog converters and related hardware. IIO communicates with user space via sysfs and a character devices. From a plain user interaction point of view this is quite intuitive, since everything is just a file. However when controlling the device from software, this can be quite painful, since you simple want to call a function or method, instead of doing string manipulation and file IO. LibIIO fills this gap, provides all sorts of device abstraction and handles all kind of IIO internals. LibIIO is cross platform and also provides different language bindings, so that you can control IIO devices from C, C++, C# or Python.

If you’re not familiar with IIO, please start reading here:

Controlling the transceiver

The code snippet below is a minimalistic example without error checking. It shows how to control the AD936x transceiver via a remote connection.

  1. Create IIO IP Network context. Instead of ip:xxx.xxx.xxx.xxx it'll also accept usb:XX.XX.X
  2. Get the AD936x PHY device structure
  3. Find and write the TX LO frequency
  4. Find and write RX baseband rate


int main (int argc, char **argv)
{
	struct iio_context *ctx;
	struct iio_device *phy;
 
	ctx = iio_create_context_from_uri("ip:192.168.2.1");
 
	phy = iio_context_find_device(ctx, "ad9361-phy");
 
	iio_channel_attr_write_longlong(
		iio_device_find_channel(phy, "altvoltage0", true),
		"frequency",
		2400000000); /* RX LO frequency 2.4GHz */
 
	iio_channel_attr_write_longlong(
		iio_device_find_channel(phy, "voltage0", false),
		"sampling_frequency",
		50000000); /* RX baseband rate 50 MSPS */
 
	receive(ctx);
 
	iio_context_destroy(ctx);
 
	return 0;
}

Receiving data

int receive(struct iio_context *ctx)
{
	struct iio_device *dev;
	struct iio_channel *rx0_i, *rx0_q;
	struct iio_buffer *rxbuf;
 
	dev = iio_context_find_device(ctx, "cf-ad9361-lpc");
 
	rx0_i = iio_device_find_channel(dev, "voltage0", 0);
	rx0_q = iio_device_find_channel(dev, "voltage1", 0);
 
	iio_channel_enable(rx0_i);
	iio_channel_enable(rx0_q);
 
	rxbuf = iio_device_create_buffer(dev, 4096, false);
	if (!rxbuf) {
		perror("Could not create RX buffer");
		shutdown();
	}
 
	while (true) {
		void *p_dat, *p_end, *t_dat;
		ptrdiff_t p_inc;
 
		iio_buffer_refill(rxbuf);
 
		p_inc = iio_buffer_step(rxbuf);
		p_end = iio_buffer_end(rxbuf);
 
		for (p_dat = iio_buffer_first(rxbuf, rx0_i); p_dat < p_end; p_dat += p_inc, t_dat += p_inc) {
			const int16_t i = ((int16_t*)p_dat)[0]; // Real (I)
			const int16_t q = ((int16_t*)p_dat)[1]; // Imag (Q)
 
			/* Process here */
 
		}
	}
 
	iio_buffer_destroy(rxbuf);
 
}
university/tools/pluto/controlling_the_transceiver_and_transferring_data.1493387985.txt.gz · Last modified: 28 Apr 2017 15:59 by Michael Hennerich

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